The present invention relates to position detection using light, and more particularly to determining the coplanarity of surface-mounted integrated circuits.
A number of methods and apparatus exist for detecting the position and shapes of objects using lasers or other light sources. In one method, light reflected from an object is focused onto a camera or a solid-state image detector having a plurality of elements. Each pixel, or element, in the detector can be monitored to determine the outline of the object being tested. In other applications, such as optical heads for reading optical discs, two or more detectors are used to detect a reflected laser beam off the optical disc. The relative intensities of light hitting the detectors is compared for focusing and tracking information. Yet another type of position detector uses a linear photo-detector which produces an output signal proportional to the position on the detector where a reflected beam of light impacts. Such detectors can be used for monitoring moving objects, such as optical discs, and for maintaining a constant thickness for a material in a manufacturing process.
In the area of integrated circuits, one type of integrated circuit is mounted flat on top of a circuit board, rather than having leads which extend through holes in the board. This type of a device is called a surface-mount device. It is essential that all the leads of such a surface-mount device be within the same plane so that it can be mounted accurately upon a circuit board. There is a need for a tester to determine the coplanarity of surface-mount devices.